What I really want to achieve is for her to not only tinker and do stuff that is interesting, but also maximize her general understanding, i.e. to make sure she

What I really want to achieve is for her to not only tinker and do stuff that is interesting, but also maximize her general understanding, i.e. to make sure she gains knowledge that is transferable. That's why I'm a bit reluctant about the front-end track (not even mentioning the whole JS framework and tooling drama). On the other hand, going for general programming topics and some theory with Python might not be nearly as much fun and might be off-putting.